Fay, Spofford & Thorndike
TOWN OF BELMONT
WINN’S BROOK SEWER OVERFLOW MITIGATON
Presentation to the
BOARD OF SELECTMAN
December 7, 2009
Fay, Spofford & Thorndike
Presentation Objectives
• Project background
• Causes of sewer overflows
• Conceptual design and modeling
• Final Design
• Opinion of probable construction cost
• Funding
• Schedule
Fay, Spofford & Thorndike
Winn’s Brook Area
• Low lying area in Northeast Belmont
• Close proximity to MWRA connection on Flanders Road
• 85% of Belmont tributary to Flanders Road
• Extensive upstream sewer system
• Two different sewer subsystems
Fay, Spofford & Thorndike
The Problem
Periodic sanitary sewer overflows and backups into basements of
homes in the Winn’s Brook Area
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Reported Backups
Dates Number Rainfall (inches)
October 1996 29 10
June 1998 42 8
March 2001 32 7
May 2006 11 12
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Causes of an IncreasedHydraulic Grade Line (HGL)
• System Capacity Constraints
• Infiltration/Inflow in Belmont– 2007 Flow Monitoring Program
• Elevated downstream HGL– Flanders Road Connection to the MWRA
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Project Timeline
• 2005 – Geographical Information System (GIS)
– InfoWorks Sewer Model• Used by Cambridge & MWRA
• 2006 – Winn’s Brook Area Study
• 2007 – State (SRF) Loan Application
• 2009 – Final Design
Fay, Spofford & Thorndike
Solution Constraints
• No transference of the problem to Cambridge or significant increase in flow to MWRA interceptor
• No transference of problem within Belmont
• Continued I/I reduction will be required– 2009 Sewer System Evaluation Survey
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Mitigation Concepts
• Increase sewer capacity
• Flow diversion
• Storage
• Isolation and Pumping
• I/I Removal
• 13 Mitigation Alternatives Modeled
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Collaboration with the City of Cambridge
• Cambridge integrated Belmont’s model into the complete downstream system model
• Key in refining the selected Alternative
• NO ADVERSE IMPACT TO CAMBRIDGE
• NO INCREASED CSO RELEASE (MWRA)
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Selected Alternative No. 12
• Isolate Winn’s Book Area during elevated HGL conditions– New sewers and diversion structures– Divert flow to an off-line pumping station
• Divert upstream flow– Dean Street– Leonard Street & Alexander Ave.
• In-line storage conduit (Dean St)– Restricted discharge
• 15% Townwide I/I reduction
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Predicted Impact at Key Manholes Outside Winn’s Brook Area
(MH rim to HGL)
Hamilton Baker Oliver Channing
Baseline
(May 2006)0.07 0.23 0.25 0.37
Alt. 12
(15 % I/I red)0.10 0.23 0.34 0.10
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Flanders RoadPredicted Discharge
May 2006
Mother’s Day Storm
Peak Discharge
MGD
24-Hour Volume
MG
Baseline 16.53 15.34
Alternative 12 16.84 14.90
Difference 1.98% -2.84%
Fay, Spofford & Thorndike
Opinion of Probable Construction Cost - Contract 3
Base Bid
Winn’s Brook Sewer Overflow Mitigation Facilities
$6.6 Million
Additive Alternates
Townwide I/I Removal
$1.4 Million
TOTAL $8.0 Million
Fay, Spofford & Thorndike
Project Funding
• $11.6 M State Revolving Loan (SRF)– ARRA “Shovel Ready” Projects
• Contract 1 – Wellington Brook Area Sewer and Storm Drain Improvements
• Contract 2 – Stony Brook Road and Woodbine Road Pump Station Replacement
• Contract 3 – Winn’s Brook Area Sewer Overflow Mitigation
Fay, Spofford & Thorndike
Winn’s Brook – Contract 3Construction Schedule
11/25/2009 - Advertised for Bid
12/21/2009 - Bids Received
01/15/2010 - Contract Execution
02/01/2010 - Notice to Proceed
07/31/2011 - Construction Complete
(18 months)
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